To estimate how quickly a restored salt marsh was accumulating sediment, environmental scientist Priya Nandakumar compared readings from surface-elevation pins with estimates derived from cesium isotope profiles. The close agreement between the pin readings, which reflect short-term changes in marsh height, and the isotope estimates calculated across several ______ the assumption that short-term measurements systematically overstate long-term marsh growth.
Which choice completes the text so that it conforms to the conventions of Standard English?